The present invention relates to methods and compositions that may be useful in treating subterranean formations, and more specifically, to methods and compositions that may be useful to prevent scale formation and/or diageneous reactivity on mineral surfaces residing or to be placed in subterranean formations.
In the production of hydrocarbons from a subterranean formation, it is sometimes desirable that the subterranean formation be sufficiently conductive to permit the flow of desirable fluids to a well bore penetrating the formation. In some cases, hydraulic fracturing treatments and/or acidizing treatments may be used to increase the conductivity of a subterranean formation. In hydraulic fracturing operations, a treatment fluid (e.g., a fracturing fluid or a “pad” fluid) is pumped into a well bore that penetrates a subterranean formation at a sufficient hydraulic pressure to create or enhance one or more pathways, or “fractures,” in the subterranean formation. The fluid used in the treatment may comprise particulates, often referred to as “proppant particulates,” that are deposited in the resultant fractures, to prevent the fractures from fully closing upon the release of hydraulic pressure, e.g., by forming a proppant pack and conductive channels through which fluids may flow to a well bore.
It is also sometimes desirable to prevent the migration of unconsolidated particulates, formation sands, and formation fines into the well bore. To this end, gravel-packing treatments may be used wherein a treatment fluid suspends a plurality of particulates (commonly referred to as “gravel particulates”) for delivery to a desired area in a well bore, e.g., near unconsolidated or weakly-consolidated formation zones, to form a gravel pack that may, inter alia, reduce the migration of particulates, formation sands, and formation fines into the well bore. One common type of gravel-packing operation involves placing a sand control screen in the well bore and packing the annulus between the screen and the well bore with the gravel particulates of a specific size to prevent the passage of formation sand. The gravel particulates act, inter alia, to prevent the formation particulates from occluding the screen or migrating with the produced hydrocarbons, and the screen acts, inter alia, to prevent the particulates from entering the production tubing in the well bore. Once the gravel pack is substantially in place, the viscosity of the treatment fluid may be reduced, inter alia, to facilitate its recovery. In some situations, fracturing and gravel-packing treatments may be combined into a single treatment (commonly referred to as “frac pack” operations). In such “frac pack” operations, the treatments are generally completed with a gravel pack screen assembly in place with the hydraulic fracturing treatment being pumped through the annular space between the casing and screen. In this situation, the hydraulic fracturing treatment ends in a screen-out condition, creating an annular gravel pack between the screen and casing. In other cases, the fracturing treatment may be performed prior to installing the screen and placing a gravel pack.
One problem that may negatively impact conductivity of a subterranean formation, even where fracturing and/or gravel packing operations have been performed, is the formation of scales on mineral surfaces in a subterranean formations. Water or aqueous treatment fluids used in subterranean operations (e.g., drilling fluids, fracturing fluids, gravel packing fluids, etc.) may contain ionized scale-forming compounds that precipitate on surfaces in subterranean formations, for example, surfaces of proppant particulates, gravel particulates, and other surfaces present where those treatment fluids are used. This scale formation may cause numerous problems, including the restriction of fluid flow through the subterranean formation. Some scales may be removed by introducing a solvent or an acidic fluid into the subterranean formation and allowed to dissolve scale on surfaces therein. However, certain types of scale may be resistant to removal with certain kinds of solvents. Moreover, certain acidic fluids may corrode portions of the formation or equipment and tubing present in the subterranean formation, dissolve and/or damage acid-soluble portions of the subterranean formation itself, generate toxic substances (e.g., H2S) in the formation, and/or be hazardous to handle or transport.
Another problem that may negatively impact conductivity of a subterranean formation is the tendency of mineral sediments in a formation to undergo chemical reactions caused, at least in part, by conditions created by mechanical stresses on those minerals (e.g., fracturing of mineral surfaces, compaction of mineral particulates). One type of these stress-activated reactions includes diageneous reactions. As used herein, the terms “diageneous reactions” and “diageneous reactivity” are defined to include chemical and physical processes that move a portion of a mineral sediment and/or convert the mineral sediment into some other mineral form in the presence of water. Any mineral sediment may be susceptible to these diageneous reactions, including silicate minerals (e.g., quartz, feldspars, clay minerals), carbonaceous minerals, and metal oxide minerals. Thus, formation sands, proppant particulates, gravel particulates, and any other mineral surfaces found in a subterranean formation may be susceptible to diageneous reactivity. The conversion and movement of mineral sediments on these surfaces may, among other things, decrease the ability of fluids to flow around those surfaces. In some cases, fracturing and gravel-packing treatments may increase diageneous reactivity, for example, by forming new mineral surfaces in newly-created fractures and/or by introducing proppant or gravel particulates that comprise additional mineral surfaces into the subterranean formation that may be even more susceptible to diageneous reactivity than the mineral surfaces naturally-occurring in the subterranean formation.